--- a/build/build-clang/clang-4-linux64.json
+++ b/build/build-clang/clang-4-linux64.json
@@ -11,11 +11,12 @@
     "libcxxabi_repo": "https://llvm.org/svn/llvm-project/libcxxabi/tags/RELEASE_401/final",
     "python_path": "/usr/bin/python2.7",
     "gcc_dir": "/builds/worker/workspace/build/src/gcc",
     "cc": "/builds/worker/workspace/build/src/gcc/bin/gcc",
     "cxx": "/builds/worker/workspace/build/src/gcc/bin/g++",
     "as": "/builds/worker/workspace/build/src/gcc/bin/gcc",
     "patches": [
       "llvm-debug-frame.patch",
-      "hide-gcda-profiling-symbols.patch"
+      "hide-gcda-profiling-symbols.patch",
+      "pr_set_ptracer.patch"
     ]
 }

--- a/build/build-clang/clang-5-linux64.json
+++ b/build/build-clang/clang-5-linux64.json
@@ -11,11 +11,12 @@
     "libcxxabi_repo": "https://llvm.org/svn/llvm-project/libcxxabi/tags/RELEASE_500/final",
     "python_path": "/usr/bin/python2.7",
     "gcc_dir": "/builds/worker/workspace/build/src/gcc",
     "cc": "/builds/worker/workspace/build/src/gcc/bin/gcc",
     "cxx": "/builds/worker/workspace/build/src/gcc/bin/g++",
     "as": "/builds/worker/workspace/build/src/gcc/bin/gcc",
     "patches": [
       "llvm-debug-frame-for-5.patch",
-      "r313872.patch"
+      "r313872.patch",
+      "pr_set_ptracer.patch"
     ]
 }

new file mode 100644
--- /dev/null
+++ b/build/build-clang/pr_set_ptracer.patch
@@ -0,0 +1,27 @@
+--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
++++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
+@@ -57,6 +57,14 @@
+ #include "sanitizer_mutex.h"
+ #include "sanitizer_placement_new.h"
+ 
++// Sufficiently old kernel headers don't provide this value, but we can still
++// call prctl with it. If the runtime kernel is new enough, the prctl call will
++// have the desired effect; if the kernel is too old, the call will error and we
++// can ignore said error.
++#ifndef PR_SET_PTRACER
++#define PR_SET_PTRACER 0x59616d61
++#endif
++
+ // This module works by spawning a Linux task which then attaches to every
+ // thread in the caller process with ptrace. This suspends the threads, and
+ // PTRACE_GETREGS can then be used to obtain their register state. The callback
+@@ -433,9 +441,7 @@
+     ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid);
+     // On some systems we have to explicitly declare that we want to be traced
+     // by the tracer thread.
+-#ifdef PR_SET_PTRACER
+     internal_prctl(PR_SET_PTRACER, tracer_pid, 0, 0, 0);
+-#endif
+     // Allow the tracer thread to start.
+     tracer_thread_argument.mutex.Unlock();
+     // NOTE: errno is shared between this thread and the tracer thread.